Glycerol is becoming an abundant chemical product as industry and consumers become increasingly reliant on fuels from biological sources. In particular, fuels (also known as biofuels) are being made from biogenic fat- or oil-containing sources and used oils obtained, for example, from cooking oil waste from restaurants and waste animal fats from food-related processing plants. Diminishing supply of readily available traditional petroleum sources, increasing prices of petroleum feeds and concerns of their impact on the environment are driving increased demands for alternative fuels such as biofuels.
To this end, hydrogenation processes for the conversion of glycerol to 1,2-propanediol have been extensively studied in recent years, and high yields have been obtained in some cases. Various catalysts have been used in these processes, including copper.
Chaminand et al., in Green Chem. 6, 2004, pages 359-361, describe the hydrogenation of aqueous glycerol solutions at 180° C. and 80 bar hydrogen pressure in the presence of supported metal catalysts based on Cu, Pd and Rh. Copper chromite, copper zinc oxide, copper aluminum oxide and copper silicon dioxide are mentioned as catalysts for such processes. Indeed, it is widely known that copper chromite is a suitable catalyst in the hydrogenation of glycerol. Copper chromite, however, is an oxide that is prone to chemical and physical degradation relative to metallic catalysts.
M. A. Dasari et al., in Appl. Chem. A: General 281, 2005, pages 225-231, describe a process for the low-pressure hydrogenation of glycerol to propylene glycol (1,2-propane diol) at a temperature of 200° C. and a hydrogen pressure of 200 psi (13.79 bar) in the presence of a nickel, palladium, platinum, copper, or copper chromite catalyst.
German Patent 524 101 has been attributed as describing a process in which glycerol is subjected to a gas-phase hydrogenation in the presence of a hydrogenation catalyst and hydrogen in considerable excess. Copper and/or cobalt catalysts can be used for the hydrogenation of glycerol. See U.S. Pat. No. 7,355,083 and WO 2007/099161. R. Connor and H. Adkins, in J. Am. Chem. Soc. 54, 1932, pages 4678-4690, describe the hydrogenolysis of oxygen-containing organic compounds, such as glycerol, to 1,2-propanediol in the presence of a copper-chromium-barium oxide catalyst.
C. Montassier et al., in Bulletin de La Societe Chimique de France 1989, No. 2, pages 148-155, describe investigations into the reaction mechanism of the catalytic hydrogenation of polyols in the presence of various metallic catalysts, such as, for example, hydrogenation of glycerol in the presence of copper.
EP 0 523 015 describes a process for the catalytic hydrogenation of glycerol for the preparation of 1,2-propanediol and 1,2-ethanediol in the presence of a Cu/Zn catalyst at a temperature of at least 200° C. In this process, the glycerol is used as an aqueous solution having a glycerol content of from 20 to 60% by weight, the maximum glycerol content in the working examples being 40% by weight.
U.S. Pat. No. 5,616,817 describes a process for the preparation of 1,2-propanediol by catalytic hydrogenation of glycerol at elevated temperature and super-atmospheric pressure, in which glycerol having a water content of not more than 20% by weight is reacted in the presence of a catalyst which comprises from 40 to 70% by weight of cobalt, if appropriate, manganese and/or molybdenum and a low copper content of from 10 to 20% by weight. The temperature is in the range of from about 180 to 270° C. and the pressure in a range of from 100 to 700 bar, preferably from 200 to 325 bar.
U.S. Patent Publication No. 2008/0045749 discloses a two step process in manufacturing 1,2-propanediol from glycerol in which the glycerol is first subjected to a dehydrogenation reaction to produce a carbonyl compound, hydroxyacetone. The second step can comprise hydrogenating the acetone to 1,2-propanediol.
U.S. Pat. No. 8,273,924 B2 which discloses the catalytic hydrogenation of glycerin with a water content of less than 20% by weight to give a 92% yield of 1,2-propanediol. The conversion of glycerol was achieved through the use of hydrogenation catalysts supported on silica, with the active composition comprising nickel, copper, and manganese. The hydrogenation reaction is carried out at a pressure and temperature range of 100 to 700 bar and 180 to 270° C., respectively. N-propanol, isopropanol and other lower alcohols were obtained as by-products.
A skeletal copper catalyst has also been used as a catalyst for the hydrogenation of glycerol to 1,2-propanediol. For example, U.S. Patent Publication No. 2011/0071323 A1 discloses a method for producing 1,2-propanediol from the catalytic hydrogenation of glycerin in a reactor operated at a steady-state conversion of preferably 60 to 95%. Glycerin is reacted with hydrogen in the presence of a copper containing, powdered catalyst in a liquid phase in a continuous stirred reactor at a pressure of 50 to 90 bar and reaction temperatures ranging from 180 to 240° C. Catalysts mentioned were Raney® copper or CuO/ZnO. 1,2-propanediol was obtained in high selectivity of up to 97% with n-propanol, isopropanol and ethanol being detected in small amounts as byproducts.
Byproducts of the glycerol hydrogenolysis to 1,2-propanediol have included 1-propanol and 2-propanols which are also useful chemicals. 1-propanol has been produced via hydroformylation of ethylene and is used mainly as a solvent, a printing ink and a chemical intermediate for the production of n-propyl acetate. See J. D. Unruh et. al., Kirk-Othmer Encyclopedial of Chemical Technology, John Wiley & Sons, NY, 2000. 2-propanol (isopropanol) has been produced by the hydration of propylene and used mainly as a solvent.
Consequently, it is desirable to provide processes for the hydrogenation of glycerol which are highly selective for 1- and/or 2-propanols and which provide these alcohols in high yield as the major products.